A massive heat dome is about to settle over much of the United States, and meteorologists say this one is different — bigger, stronger, and longer-lasting than what most Americans are used to seeing in the summer months. The National Weather Service is describing the coming conditions as “significant and dangerous.”
The heat wave is expected to kick off this weekend and stick around for at least a week, with some parts of the country not seeing relief until the final days of July. Temperatures across many regions could run 15 to 25 degrees Fahrenheit — or 8 to 14 degrees Celsius — above seasonal norms, and that includes overnight lows, which experts say is particularly alarming.
“This upcoming heat wave does look pretty remarkable,” said Daniel Swain, a climate scientist with University of California Agriculture and Natural Resources. “This is going to be a long duration, widespread and high-intensity heat event that’s going to affect millions of people for over a week.”
The heat dome works by trapping hot air beneath a high-pressure system, much like a pot lid holds in steam, while simultaneously blocking the cooling effects of wind and rain. It is expected to initially set up over the Northern Plains, but its sheer size means it could cover as much as two-thirds of the continental U.S. Though the East Coast may initially be spared, the dome is expected to shift over the next 10 days or more and could eventually stretch from coast to coast.
This weekend, forecasters are calling for record-breaking triple-digit temperatures in Nevada, Utah, Colorado, Wyoming, Idaho, Montana, North Dakota, and South Dakota.
The National Weather Service is projecting that more than 90 local temperature records across the country could be tied or broken by Wednesday alone. Roughly two-thirds of those records are expected to be overnight heat records — a particularly troubling trend because the body needs cooler nighttime temperatures to recover from daytime heat exposure.
“Nights can be just as dangerous as days. If you don’t get heat relief at night, that’s going to spill out into your daytime experience and become extremely dangerous,” warned meteorologist Bob Henson of Yale Climate Connections. “Heat is not to be played with. It’s just as dangerous as a tornado or hurricane that can kill you just as easily, just in a quiet and different way.”
Swain emphasized that what truly sets this heat wave apart is its geographic reach and how long it is expected to linger. In recent weeks, serious heat events have already hammered Europe, the U.S. East Coast, and the Southeast. He noted that any part of the country that managed to avoid those earlier July heat waves is now squarely in the crosshairs of this one.
In the Southeast, the situation could be especially unusual. Climate Central meteorologist Shel Winkley explained that rain sneaking in along the southern edge of the heat dome could create a strange weather combination — record-shattering nighttime heat paired with below-normal daytime temperatures, all driven by high humidity and added moisture.
The National Weather Service is already predicting record nighttime warmth from Texas to Florida to North Carolina on Saturday. In cities including Fort Lauderdale, Miami, Tampa, Galveston, and Charleston, South Carolina, overnight temperatures are not expected to dip below 80 degrees Fahrenheit — or 27 degrees Celsius.
While summer heat domes are not rare, Winkley said this one stands out for its intensity and its unusually northern position. It is expected to set records for the sheer amount of high pressure it contains.
Swain added that drought conditions are helping fuel the event’s staying power. Dry soil and air hold less moisture, which would otherwise help slow the warming process. Instead, the dry conditions heat the air faster, which in turn worsens drought — a vicious cycle that also increases the risk of wildfires in areas already dealing with dry conditions.
While a recently formed El Niño weather pattern is too new to significantly influence this particular heat wave, all three meteorologists agreed that human-caused climate change — driven by the burning of coal, oil, and natural gas — is clearly playing a role.
“We know that heat waves are becoming more intense, they’re lasting longer, they’re covering larger areas than they used to because of human-caused climate change,” Swain said. “And so when we see an event like this, we know there is at least a partial contribution by the long-term warming trend.”
Climate Central analyzed the forecast using 20 different computer models, comparing expected temperatures to what would occur in a world without greenhouse gas-driven warming. Their Climate Shift Index found that a 20,000-square-mile stretch of the country — from Southern California to northern Minnesota, home to 24 million people — will this weekend experience heat that is at least five times more likely to occur because of climate change. Similar findings were recorded for the East Coast heat wave around the July 4th weekend and the recent Southeast heat event.
“Using attribution science we know that those temperatures would be virtually impossible without the influence of climate change,” Winkley said.
